Hydraulic fluid

ABSTRACT

A TWO-PHASE HYDRAULIC FLUID COMPOSITION WHICH COMPRISES (A) A CONVENTIONAL AQUEOUS HYDRAULIC FLUID BASE AS A FIRST PHASE AND (B) A LIQUID HAVING A SPECIFIC GRAVITY LESS THAN THAT OF THE AQUEOUS HYDRAULIC FLUID BASE (A) AS A SECOND PHASE WHICH LIQUID (B) IS IMMISCIBLE WITH BASE (A) AND FORMS A SUPERNATANT LAYER FLOATING ON THE SURFACE OF THE AQUEOUS BASE (A).

United States l atent Cflice 3,580,847 HYDRAULIC FLUID Matthew A. Boehmer, Allen Park, and Jerrold F. Maxwell, Trenton, Mich. (both Wyandotte Chemicals Corp., Wyndotte, Mich. 48192) No Drawing. Filed June 16, 1967, Ser. No. 646,498 Int. Cl. C091: 3/00 US. 'Cl. 252-75 7 Claims ABSTRACT OF THE DISCLOSURE A two-phase hydraulic fluid composition which comprises (A) a conventional aqueous hydraulic fluid base as a first phase and (B) a liquid having a specific gravity less than that of the aqueous hydraulic fluid base (A) as a second phase which liquid (B) is immiscible with base (A) and forms a supernatant layer floating on the surface of the aqueous base (A).

This invention relates to hydraulic fluid compositions for use in devices and systems for the transmission of mechanical energy by fluid pressure.

Certain fluids, known as hydraulic fluids, are used by certain technologies as mechanical power or pressure transmitting media. In the prior art it was recognized that hydraulic fluids in general should be uoncorrosive, nonfoaming, stable liquids which do not congeal at the low temperatures encountered in their use and do not separate or gasify at the elevated temperatures to which they may be subjected. It was also considered important that they should have suflicient viscosity over a wide temperature range to permit eflicient operation of the mechanism.

Water is historically the oldest fluid used for this purpose and is still widely employed. However, at atmospheric pressure, water freezes at 32 F. and for many applications the fluid may be subjected to temperatures below this point. Since the advent of petroleum oils of suitable quality, such oils have also been extensively utilized in this application. Petroleum oils are very suitable materials for this purpose and much hydraulic equipment has been designed and manufactured for use with these oils. Petroleum oils have the advantages over water of having a more suitable viscosity, lubricating properties, and they are relatively noncorrosive. Petroleum oils, however, have the major disadvantage of being flammable and may thereby create fire hazards. For example, in industrial operations, such as the die casting of metals, the heavy casting machinery or the controls therefor are operated largely by hydraulic means. The hydraulic fluids used in such apparatus have frequently been a source of fire and danger since a leak or ruptured fluid line may spray fluid onto a surface having a sufliciently high temperature to ignite the fluid.

In recent years, new types of hydraulic fluids, which are less flammable, have been developed to operate in the machinery designed for petroleum hydraulic oils. One of the major generic types of these fluids is the so-called water-glycol or Hydrolube fire-resistant hydraulic fluid. These fluids contain the major components of glycol, water and a polymeric viscosity control agent. They have, as lesser components, additives to impart special properties such as lubricity and corrosion resistance to the fluid. A hydraulic fluid of this type is disclosed in the Zisman et 211. patent, US 2,602,780, wherein the glycols employed are any of the common glycols or glycol ethers having 2 to about 14 carbon atoms.

Within any hydraulic system, there will be found such metals as iron, brass, solder, bronze, aluminum, zinc, cadmium, and other more or less commonly used metals. The presence of several metals in a single hydraulic sys- 3,580,847, Patented May 25, 1971 tern presents the possibility of the formation of a large number of electrical couples within the system thereby providing undesirable corrosion conditions.

Within the common hydraulic system, there is always at some point a reservoir for excess fluid. Such a reservoir is never full and being a closed container it will define a vapor phase above the fluid contained therein. Even within the simplest hydraulic systems, humid corrosion within such a space presents a serious problem. In the more complex systems, found in military or commercial aircraft or in naval vessels where service conditions are extremely severe and the system is exceedingly complex, the corrosion problem is correspondingly more diflicult. The parts are frequently machined to fine tolerances and the slightest corrosion changes dimensions and upsets operation. Accordingly, it is well known to those skilled in the art to provide corrosion inhibitors for such hydraulic fluids. However, even such fluids containing corrosion inhibitors possess certain inherent disadvantages.

More specifically, hydraulic fluids are heated by mechanical and fluid friction when they are in use. This results in a buildup of heat. Usually some means is provided to dissipate the heat, but hydraulic fluids still operate generally in the range of -180 F. At these elevated temperatures, the evaporation of water and additives be comes a problem when the prior art water-glycol hydraulic fluids are employed.

The evaporation of water creates two problems. First, the water condenses on the reservoir and other surfaces and irregularities in the vapor pockets above the fluid, causing rusting. Second, the loss of water results in a fluid composition change. This loss is accelerated by the nature of the hydraulic system which uses more fluid at some times than at others, such as when cylinders are being extended, and which therefore exhibits a rising and falling of the level of fluid in the reservoir. This results in air being pumped into the reservoir and fluid vapor being pumped out, thereby losing the vapor irretrievably from the system. The composition change results in a fluid of excessive viscosity for use in the hydraulic system, since the more viscous components of the fluid are retained, and in loss of fire resistance.

To minimize rusting of equipment located in the vapor phase as explained above, volatile corrosion inhibitors are generally incorporated in water-based fluids. They do not entirely prevent rusting, but inhibit it to a certain extent. They are evaporated out of the fluid in the same manner as the water. Since they are normally basic amine compounds, their loss results in acidification of the fluid. This acidifying of the fluid results in liquid phase corrosion; loss of wear preventive properties; and loss of vapor phase corrosion protection, since the vapor phase amine becomes depleted and what remains becomes less available due to its greater aflinity for the acidic fluid.

Heretofore, users of water-based fluids have had to periodically analyze for depletion of water and amine, and to replenish the depleted water and additive. This requirement for maintenance is one of the drawbacks of water-based fluid use. Another method of partially controlling the evaporation has been to operate the system at temperatures lower than normally encountered in hydraulic fluids. However, this often adds to the expense since additional heat exchange equipment may be required.

As mentioned above, vapor phase rusting is a problem in water-based fluid use, and vapor corrosion additives are used to minimize the corrosion. However, the present additives (amines) are only marginal in their effectiveness, controlling the rusting to a certain extent rather than eliminating it.

Foam is often a problem with hydraulic fluids. Air entrapment in the fluid results in loss of function, since the basic principles upon which hydraulic technology is founded assume that the transmitting fluid is incompressible. In actual practice, air entrapment causes erratic action, sluggish action, loss of function, high pump wear, and excessive noise and heat build-up. Since the hydraulic system has various interfaces of fluid and air, (such as in the open reservoir; at packings, glands, scale and gaskets; in accumulators, etc.) and is dynamic, air entrainment is very likely to occur. Any air introduced into the fluid must be eliminated rapidly to prevent the aforementioned malfunctions. So-called defoamers are commonly incorporated in the fluids to achieve this purpose, Because of the nature of the additives incorporated into waterbased hydraulic fluids, foam control has sometimes been a problem in the past. In addition, foam considerations have prevented the incorporation of many efficacious wear and corrosion preventive additives into the fluid.

Accordingly, it is a purpose of this invention to provide a novel water-based hydraulic fluid wherein the problems presented by evaporation of water from the hydraulic fluid resulting in increased viscosity and vapor phase rusting as well as those caused by the evaporation of volatile corrosion inhibitors resulting in the acidification of the fluid and loss of vapor phase corrosion protection are eliminated or substantially reduced.

These and other purposes are accomplished in accordance with this invention by providing a two-phase hydraulic fluid composition consisting essentially of (A) an aqueous hydraulic fluid base and (B) a liquid having a specific gravity less than that of the hydraulic fluid base (A) and which is immiscible with the base (A), floating on the surface of base (A). It is preferred that this hydraulic fluid consist essentially of about 95 to 99.9% by weight of the aqueous hydraulic fluid base (A) and 0.1 to 5.0% by weight of the floating liquid (B).

The hydraulic fluid base (A) is a conventional aqueous hydraulic fluid containing preferably about 35 to 70% by weight of water and about to 50% by weight of a water-miscible freezing point depressant. It is preferred to employ water-soluble polyhydric alcohols or ethers as freezing point depressants. These may be any of the common glycols or glycol ethers having 2 to about 14 carbon atoms such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol ethers such as the ethyl, methyl, propyl, and butyl ethers thereof, and similar ethers of diethylene and triethylene glycol. In general, it is preferred to use the simpler compounds as represented by the polyhydric alcohols such as ethylene glycol, propylene glycol, 'butylene glycol, glycerine, and diethylene glycol for they are easily obtainable and blend easily with water to give very low-freezing mixtures which form good bases for the fluid compositions. As the basis of the hydraulic fluid composition, it is preferable to use proportions of water and polyhydric alcohol which will give in combination a very low freezing point for a given mixture.

The base fluid may also contain a conventional soluble organic polymeric thickener. It is preferred to include the thickener in the base (A) in amount of about 1 to 50 Weight percent.

The expression soluble organic polymeric thickener, as used herein, refers to those thickeners which are soluble in water-polyhydric alcohol ether mixtures.

Soluble thickeners for hydraulic fluids are well known to those skilled in the art as can be seen by reference to US. Patent No. 2,462,694 which discloses a large number of such soluble thickeners in columns 2, 3 and 4 thereof. For the hydraulic fluids of the instant invention, soluble thickeners with molecular weights in excess of 6000 which may range up to 100,000 may be employed. However, soluble thickeners of a molecular weight of about 10,000 to 25,000 are preferred.

An excellent soluble organic polymeric thickener for use with the hydraulic fluid of this invention comprises a copolymer of ethylene oxide and 1,2-propylene oxide or 1,3-propylene oxide, preferably one containing more than 50 mol percent of ethylene oxide and less than 50 mol percent of the propylene oxide, coplymerized to a thick fluid polymer. A thickener having the optimum water solubility, viscosity, shear strength, and other properties desirable in a hydraulic fluid composition may be made by copolymerizing about 75 mol percent of ethylene oxide and about 25 mol percent of isopropylene oxide to a molecular weight of about 10,000 to 25,000. The polymer thus formed thickens the aqueous base to the desired viscosity when added in only a small proportion. The higher molecular weight polymers are the more effective thickening agents. The polymers have a composition which can be indicated as follows:

in which n and q are whole numbers, and n/q is greater than 1, which, it is clear, is characterized by the frequent random recurrence of methyl group branches.

The hydraulic fluid base may include solvents with sufliciently high flash points such as formamide. The aqueous type hydraulic fluid base (A) may be formulated with conventional additives such as buffering agents, antifoaming agents, antiwear agents, and corrosion inhibitors. Suitable corrosion inhibitors include the alkali metal benzoates, pelargonates, nitrates, nitrites, organo-phosphates, and fatty acid salts; the mercapto-benzothiazoles and benzotriazole; amines such as morpholine, dimethylaminoethanol, diethylaminoethanol, triethanolamine, diethanolamine, monoethanolamine, dibutylamine, etc.; phosphates and other salts of the said amines.

The floating liquid (B) may consist of any organic liquid which 1) does not interfere with normal fluid function, (2) has a lower density than the fluid, (3) is substantially non-evaporative, (4) spreads to form a layer over the surface of the fluid, (5) is relatively impermeable to water and amine vapors, (6) is immiscible with the fluid, (7) possesses enough lubricity such that induction into the hydraulic system would not cause damage, (8) is .nonfoaming, and (9) is noncorrosive in both liquid and vapor phase. Two efficacious materials for Component (B) include mineral oil and cetyl alcohol. Other materials which may be employed include silicones, fatty alcohols, and polyalkylene glycols, preferably having about 3 to 10 carbon atoms.

Additives can be blended into Component (B) to achieve additional desired properties. For example, polypropylene glycol or other polyalkylene glycols may be added to mineral oil to enhance its water resistance and demulsibility; oxidation inhibitors may be added to insure long life; surfactants may be added to cause better spreading on the surface; corrosion inhibitors may be added, etc.

The immiscible floating liquid (B) may incorporate a foam suppressor which may be any antifoam agent which minimizes foam production and accelerates the de-aeration of the fluid. Suitable antifoam agents are conventional silicone antifoam agents, aliphatic alcohols of 10 carbons or more, organic phosphates and phthalates, conventional nonionic synthetic detergents, etc., having the desired properties. More specifically, it must be a defoamer for the hydraulic fluid and must be soluble with other components in the floating liquid.

Nonionic synthetic detergents which may advantageously be employed in the compositions of the invention as antifoam agents include polyoxyalkylene adducts of hydrophobic bases. Ethylene oxide, for example, is condensed with the hydrophobic base in an amount sufficient to impart water solubility and surface active properties to the molecule being prepared. The exact amount of ethylene oxide condensed with the hydrophobic base will depend upon the chemical characteristics of the base employed and is readily apparent to those of ordinary skill in the art relating to the synthesis of oxyalkylene surfactant condensates. In general, the amount of ethylene oxide is less than 20% of the weight of the hydrophobic base.

Typical hydrophobic bases which can be condensed with ethylene oxide in order to prepare nonionic surface active agents include monoand polyalkyl phenols and the compounds prepared by condensing polyoxypropylene onto a base having from about 1 to 6 carbon atoms and at least one reactive hydrogen atom. The hydrocarbon ethers such as the benzyl or lower alkyl ether of the polyoxyethylene surfactant condensates are also advantageously employed in the compositions of the invention.

Further suitable nonionic surface active agents are the polyoxyethylene esters of higher fatty acids having from about 8 to 22 carbon atoms in the acyl group. Typical products are the polyoxyethylene adducts of tall oil, rosin acids, lauric, stearic and oleic acids and the like. Additional nonionic surface active agents are the polyoxyethylene condensates of higher fatty acid amines and amides having from about 8 to 22 carbon atoms in the fatty alkyl or acyl group. Illustrative products are coconut oil, fatty acid amines and amides condensed with ethylene oxide.

Other suitable polyoxyethylene nonionic surface active agents are the ethylene oxide adducts of higher aliphatic alcohols and thioalcohols having from about 8 to 22 carbon atoms in the aliphatic portion. A typical product is tridecyl alcohol condensed with ethylene oxide.

Other suitable nonionic surface active agents are cogeneric mixtures of conjugated polyoxyalkylene compounds containing in their structure at least one rhydrophobic oxyalkylene chain in which the oxygen/carbon atom ratio does not exceed 0.40 and at least hydrophilic oxyalkylene chain in which the oxygen/carbon atom ratio is greater than 0.40. In accordance with the preferred practice of this invention, the hydrophilic oxyalkylene chain is less than 20% of the total weight of the oxyalkylene chain.

Polymers of oxyalkylene groups obtained from propylene oxide, butylene oxide, amylene oxide, styrene oxide, mixtures of such oxyalkylene groups with each other and with minor amounts of polyoxyalkylene groups obtained from ethylene oxide, butadiene dioxide, and glycidol are illustrative of hydrophobic oxyalkylene chains having an oxygen/carbon atom ratio not exceeding 0.40. Polymers of oxyalkylene groups obtained from ethylene oxide, butadiene dioxide, glycidol, mixtures of such oxyalkylene groups with each other and with minor amounts of oxyalkylene groups obtained from propylene oxide, butylene oxide, amylene oxide and styrene oxide are illustrative of hydrophilic oxyalkylene chains having an oxygen/carbon atom ratio greater than 0.40.

Among the conjugated polyoxyalkylene compounds which can be used in the compositions of the invention are those which correspond to the formula:

wherein Y is the residue of organic compound having from about 1 to 6 car-bon atoms and one reactive hydrogen atom, 11 has an average value of at least about 6.4 as determined by hydroxyl number and m has a value such that the oxyethylene portion constitutes up to about 20 weight percent of the molecule. These surface active agents are more particularly described in US. Pat. No. 2,677,- 700.

Other conjugated polyoxyalkylene surface active agents which are most advantageously used in the compositions of the invention correspond to the formula:

wherein Y is the residue of an organic compound having from about 2 to 6 carbon atoms and containing x reactive hydrogen atoms in which x has a value of at least about 2, n has a value such that the molecular weight of the polyoxypropylene hydrophobic base is at least about 900 and m has a value such that the oxyethylene content of the molecule is up to about 20 weight percent. Compounds falling within the scope of the definition for Y include, for example, propylene glycol, glycerine, pentaerythritol, trimethylolpropane, ethylene diamine, and the like. As already noted, the oxypropylene chains optionally, but advantageously, contain small amounts of ethylene oxide and the oxyethylene chains also optionally, but advantageously, contain small amounts of other alkylene oxides such as propylene oxide and butylene oxide. These compositions are more particularly described in US. Pat. No. 2,674,619. These polyoxyalkylene surface active agents include the nitrogen containing polyoxyalkylene compounds of US. Pat. No. 2,979,528. Suitable polyoxyalkylene compounds are also disclosed in US. Pat. No. 2,425,755.

The floating liquid (B) may also include a vapor phase corrosion inhibitor which may consist of any of the common vapor phase corrosion inhibitors such as amines, acids, amine-acid complexes, and other materials commonly known to those skilled in the art. Conventional vapor phase corrosion inhibitors include morpholine, dibutylamine, and cyclohexylamine and combinations of them may be employed. Such inhibitors are disclosed by Baker in Volatile Rust Inhibitors, Industrial and Engi neering Chemistry, vol. 46, December 1954, p. 2592.

Certain long-chain fatty acids and derivatives thereof may be employed as antiwear agents and rust preventatives and, preferably, are incorporated in the base liquid (A), for example, oleic acid, stearic acid, lauric acid, capric acid, and corresponding fatty oil or glycerides and the like along with alkali metal or amine soaps of fatty acids. Conventional buffering agents such as alkali metal hydroxides, alkali metal salts, and straight chain fatty acids such as alkali metal acetates, etc., may be employed to maintain reserve alkalinity. It is preferred to maintain the pH of these hydraulic fluids in a range of from about 7 to 11.

The range of proportions of the additives may vary widely. For example, good results are obtained with a hydraulic fluid which consists essentially of the abovedescribed aqueous hydraulic fluid base (A) containing as additives about 0.02 to 2.5% of at least one corrosion inhibitor, about 0.0005 to 0.1% of at least one antifoaming agent, about 0.2 to 1.0% of at least one antiwear agent, and 0.2 to 3.0% of at least one buffering agent and an immiscible floating liquid (B), as above described, containing 10 to by weight of at least one antifoaming agent and 0.1 to 50% by Weight of at least one vapor phase corrosion inhibitor.

The practice of this invention will be more completely understood by reference to the following examples.

EXAMPLE 1 A hydraulic fluid base (A) was formulated as shown in Table I below.

Viscosity, SUS at 100 F.205. Spec. gravity 60/ 60 F.-1.079.

Copolymer of about 75 mol percent ethylene oxide and about 25 mol percent of 1,2-propylene oxide copolymerized to a thick fluid polymer having an average molecular weight of about 17,000.

Test results on the above base fluid (A) are shown in Table II below without a floating liquid (B) (Test No. 1), with a mineral oil floating liquid (B) by itself (Test No. 2), and the mineral oil containing a foam suppres- 7 sant (Test No. 3), a vapor phase corrosion inhibitor (Test No. 4), and both (Test No. 5). The amounts of floating liquid (B) are in percent by weight of the hydraulic base.

Polymer No. 1 is a polyoxyethylene-polyoxypropylenepolyoxyethylene block copolymer wherein the average molecular weight of the polyoxypropylene base is about 3250 and the polyoxyethylene content of the molecule is about Weight percent.

VPI (Vapor Phase Inhibition) corrosion ratings were determined as follows:

SAE 1020 steel panels of 1 /2" x 3 X thick were sanded to remove all surface corrosion, washed thoroughly with acetone, and suspended, as described below, in the vapor area above 75 cc. of test fluid contained in a vertical 2" x 16" test tube. Three panels were suspended by cotton string, one above the other, with the lower two suspended from the one directly above and the top one suspended from a glass hook located in the center of a rubber stopper used to seal the test tube. In order to tie the string to the panels, A" holes were drilled in opposite ends of the panels, /2" from the center of the 1 /2" side. The panels were located in the test tube in a manner wherein the bottom panel was suspended so that it touched the test tube with both corners of one of its 1 /2" sides. The middle panel was suspended such that its center was 6 above the center of the bottom panel and the top panel was suspended with its center 6" above the center of the middle panel. The rubber stopper was drilled near the edge and a 6 mm. glass tube, bent to allow condensed material to run down the sides of the test tube and extending 10 above the top of the stopper, was inserted. The test tube, rubber stopper, and panels were assembled and the bottom of the test tube was placed in a 130 F. bath to a depth of 5". The assembly was left in the bath for 10 days at which time the panels were given a VPI Corrosion Rating as follows:

Poor 10% corroded Fair2l0% corroded Good 2% corrodedsome corrosion spots Excellentno corrosion total Weight loss Percent evaporation loss= EXAMPLES 2-6 Additional examples of hydraulic fluids embodying the principles of this invention are illustrated by fluids wherein various floating liquids (B), having the composition set forth in Table III below, float on the hydraulic fluid 8 base (A) of Table I above. The amounts are in percent by weight of the hydraulic fluid base.

TABLE III Floating liquid (B) Material Percent Polymer No. 2 is a polyoxyethylene-polyoxypropylenepolyoxyethylene block copolymer wherein the average molecular weight of the polyoxypropylene base is about 1750 andthe polyoxyethylene content of the molecule is about 10 weight percent.

Polymer No. 3 is a polyoxyethylene-polyoxypropylene adduct of glycerine wherein the average molecular weight of the polyoxypropylene units is about 3250 and the polyoxyethylene content of the molecule is about 10 weight percent.

While there has been shown and described hereinabove the present preferred embodiments of this invention, it is to be understood that various changes, alterations and modifications can be made thereto without departing from the spirit and scope thereof as defined in the appended claims.

What is claimed is: 1. A two-phase hydraulic fluid composition consisting essentially of Aabout 95.0 to 99.9% by weight of an aqueous hydraulic fluid base, said aqueous hydraulic fluid base consisting of (1) from about 35 to 70% by weight of water, (2) from about 10 to 50% by weight of a water-soluble polyhydric alcohol freezing point depressant selected from the group consisting of glycols and glycol ethers having from 2 to about 14 carbon atoms, and (3) from about 1 to 50% by weight of a water-soluble polymerized alkylene ether thickener, having a molecular weight of from about 6,000 to 100,000, and

B-about 0.10 to 5.0% by weight of a liquid selected from the group consisting of mineral oil and cetyl alcohol having a specific gravity less than that f said hydraulic fluid base (A) and which is immiscible with said base (A) floating on the surface of said base (A).

2. The hydraulic fluid of claim 1 wherein said liquid (B) contains a foam suppressant soluble therewith and selected from the group consisting of silicone antifoam agents, organic phosphates, organic phthalates and nonionic synthetic detergents which are ethylene oxide adducts of a hydrophobic base having an ethylene oxide content less than 20% of the weight of the hydrophobic base.

3. The hydraulic fluid of claim 1 wherein said liquid (B) includes a vapor phase corrosion inhibitor selected from the group consisting of morpholine, dibutylamine, cyclohexylamine, hexylamine, and mixtures thereof.

4. The hydraulic fluid of claim 1 wherein said liquid (B) includes a foam suppressant soluble therewith and selected from the group consisting of silicone antifoam agents, organic phosphates, organic phthalates and nonionic synthetic detergents which are ethylene oxide adducts of a hydrophobic base having an ethylene oxide content less than 20% of the weight of the hydrophobic base and a vapor phase corrosion inhibitor selected from the group consisting of morpholine, dibutylamine, cyclohexylamine, hexylamine and mixtures thereof.

5. The hydraulic fluid of claim 1 wherein said polyhydric alcohol freezing point depressant is ethylene glycol.

6. The composition of claim 4 wherein the amount of said vapor phase corrosion inhibitor is from about 0.1 to 50% by weight of said liquid (B).

7. The composition of claim 6 wherein said hydraulic fluid base consists essentially by weight of about 31.0% ethylene glycol, 1.3% mixed isopropylaminoethanol, 0.7% lauric acid, 0.2% Z-mercaptobenzothiazole, 0.2% potassium hydroxide, 1.0% potassium nitrate, 49.3% water, and 16.3% of said water soluble organic polymeric thickener.

References Cited UNITED STATES PATENTS 2,602,780 7/1952 Zisman et al. 25273 2,751,355 6/1956 Clark 25275 2,768,955 10/1956 Heisig 25278 2,951,038 8/1960 Holzinger 25273 3,344,075 9/1967 Scott 25275 2,462,694 2/ 1949 Walker 25275 3,346,501 10/ 1967 Boehmer 25273 LEON D. ROSDOL, Primary Examiner D. SILVERSTEIN, Assistant Examiner US. Cl. X.R. 25273, 77, 78 

